[PATCH 1/2] NFSv4/flexfiles: fix NULL dereference for NFSv4.0 data servers

[Jeuk Kim]

flexfiles accepts NFSv4.0 data servers, but two NFSv4 code paths assume
the data server client has a session. Unlike NFSv4.1+, an NFSv4.0 client
has no session (clp->cl_session is NULL; it uses clp->cl_slot_tbl), so
I/O to a v4.0 flexfiles DS oopses:

  - nfs4_init_ds_session() dereferences clp->cl_session->session_state
    while seeding the DS lease. It also only seeds cl_lease_time when
    NFS4_SESSION_INITING is set; without a session that never happens, so
    cl_lease_time stays 0 and nfs4_renew_state() busy-loops, requeuing
    every 5 seconds. Seed the lease whenever there is no session and
    return before touching session state.

  - ff_layout_async_handle_error_v4() dereferences
    clp->cl_session->fc_slot_table on every DS I/O error. Fall back to the
    v4.0 transport slot table (clp->cl_slot_tbl) when there is no session.

Fixes: a7878ca14008 ("nfs: flexfilelayout: remove v3-only data server limitation")
Signed-off-by: Jeuk Kim <jeuk20.kim@xxxxxxxxxxx>
---
 fs/nfs/flexfilelayout/flexfilelayout.c |  3 ++-
 fs/nfs/nfs4session.c                   | 16 +++++++++++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
index c4aa995026f6..ef26fcab9c10 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.c
+++ b/fs/nfs/flexfilelayout/flexfilelayout.c
@@ -1322,7 +1322,8 @@ static int ff_layout_async_handle_error_v4(struct rpc_task *task,
 	struct pnfs_layout_hdr *lo = lseg->pls_layout;
 	struct inode *inode = lo->plh_inode;
 	struct nfs4_deviceid_node *devid = FF_LAYOUT_DEVID_NODE(lseg, idx, dss_id);
-	struct nfs4_slot_table *tbl = &clp->cl_session->fc_slot_table;
+	struct nfs4_slot_table *tbl = nfs4_has_session(clp) ?
+		&clp->cl_session->fc_slot_table : clp->cl_slot_tbl;
 
 	switch (op_status) {
 	case NFS4_OK:
diff --git a/fs/nfs/nfs4session.c b/fs/nfs/nfs4session.c
index 5c128957a0a4..993f0db7cf5e 100644
--- a/fs/nfs/nfs4session.c
+++ b/fs/nfs/nfs4session.c
@@ -632,16 +632,22 @@ int nfs4_init_ds_session(struct nfs_client *clp, unsigned long lease_time)
 	int ret;
 
 	spin_lock(&clp->cl_lock);
-	if (test_and_clear_bit(NFS4_SESSION_INITING, &session->session_state)) {
-		/*
-		 * Do not set NFS_CS_CHECK_LEASE_TIME instead set the
-		 * DS lease to be equal to the MDS lease.
-		 */
+	/*
+	 * Do not set NFS_CS_CHECK_LEASE_TIME instead set the
+	 * DS lease to be equal to the MDS lease.
+	 *
+	 * A v4.0 DS has no session, so seed the lease every time.
+	 */
+	if (!session ||
+	    test_and_clear_bit(NFS4_SESSION_INITING, &session->session_state)) {
 		clp->cl_lease_time = lease_time;
 		clp->cl_last_renewal = jiffies;
 	}
 	spin_unlock(&clp->cl_lock);
 
+	if (!session)
+		return 0;
+
 	ret = nfs41_check_session_ready(clp);
 	if (ret)
 		return ret;
-- 
2.43.0